Some effects of light on the interconversion of metabolites in green leaves

When Chlorella is allowed to photosynthesize for 30 sec. in the presence of labelled carbon dioxide it does not incorporate radioactivity into glutamate and isocitrate. After the removal of 14CO2, appreci- able activity does appear in these compounds if the algae are then kept for a further 150 sec. in the dark but not if they are maintained for the same length of time in the light. From these results (Calvin, 1949) and similar results (Benson & Calvin, 1950; Calvin & Massini, 1952) it was concluded that products newly formed in photosynthesis could not readily enter Krebs-cycle reactions in the light. Calvin & Massini (1952) attributed this to an inhibition of pyruvate oxidation.